The present invention relates to certain compositions and processes useful for minimizing biological and colloidal fouling. The present invention further relates to compositions and methods for minimizing biological and colloidal fouling in aqueous systems that use separation membranes. General embodiments of such aqueous systems, include but are not limited to, nanofiltration, ultrafiltration, microfiltration and particularly reverse osmosis processes. The compositions of the present invention preferably show unexpected efficacy in minimizing biological and colloidal fouling.
Reverse osmosis (RO) is a process commonly used in commercial, industrial, and home liquid purification systems. RO processes purify liquids that contain undissolved and dissolved impurities. The liquid to be purified is passed over a RO membrane. The "permeate" passes through the reverse osmosis membrane and is collected as purified liquid, while the remaining liquid, or "concentrate" is discarded or further processed. The successful practice of a RO process is inhibited by accumulating colloidal dispersions and biofouling.
Biofouling can be considered as one of the last major unresolved problems affecting RO processes. This is because the most common RO membrane type in use today cannot tolerate chlorine or other oxidizing biocides. For this reason, chlorine must generally be removed from the feedstreams to these systems. However, without the presence of a chlorine residual, microorganisms quickly colonize and biofoul membrane surfaces. The approach of the industry thus far has been either to ignore the problem and accept high operating costs due to biofouling, or to add non-oxidizing biocides to these plants. It has been estimated that the cost of biofouling may total as high as $0.25 per 1000 gallons of RO permeate produced. This high cost makes biofouling control by non-oxidizing biocides economically attractive.
However, there are a significant number of drawbacks to many of the non-oxidizing biocides currently available. Specifically, non-oxidizing biocides are known to be highly toxic, incompatible with RO membranes, produce unwanted side reactions with other treatment chemicals or feedwater constituents, and/or adversely affect downstream processes where excess biocides passes through RO membranes.
Accordingly, there is a need in the art for a biocidal composition that overcomes these and other problems.